Degradation of Organic Micropollutants by Hydrodynamic and/or Acoustic Cavitation

In recent years, micropollutants have become an emerging issue in natural water bodies, especially in industrialized countries. To treat those micropollutants, different advanced oxidation processes were developed and optimized. Some of the advanced oxidation processes need additional chemicals (catalysts, oxidation agents, pH control), which have to be separated, (re)activated, or degraded after the treatment process often followed by a neutralization step accompanied with high salt loads. Cavitation processes belong to the group of advanced oxidation processes, due to the formation of highly reactive hydroxyl radicals by the homolytic cleavage of water molecules in the cavitation bubbles. Cavitation processes do not need any additional chemicals and do not rely on the salt content or turbidity. Moreover, the formation of hydroxyl radicals takes place in the whole volume of the treated water and is not restricted to a specific surface. However, the energy demand of cavitation processes is higher compared to other advanced oxidation processes. Therefore, new cavitation-based processes have to be developed to overcome the disadvantages. One possibility is the use of a combination of hydrodynamic and acoustic cavitation in one reactor, the so-called hydrodynamic-acoustic-cavitation. Within this, the effect of different parameters on the hydroxyl radical formation within a HAC setup is discussed and compared with literature data. Therefore, the oxidation of salicylic acid via hydroxyl radicals was used as model reaction (salicylic acid dosimetry). Moreover, a comparison concerning the synergy and the energy efficiency was done and research desiderata were derived.